1. Field of the Invention
The present invention relates to a wire dot matrix printer head and, more particularly, relates to an inking system for supplying liquid ink directly to printing wires.
2. Description of the Prior Art
Generally, in a wire dot matrix printer requiring no ink ribbon, an ink absorbent member is arranged in a printer head thereof so as to come into direct contact with each of printing wires to thereby supply ink to the printing wires. The ink absorbent member is supplied with ink from an ink reservoir vessel via a capillary path member or a pipe. The wire dot matrix printers of this type are disclosed in, for example, U.S. Pat. Nos. 4,194,846, 4,279,519 and 4,353,654, and Japanese Patent Unexamined Publication Nos. 56-11272 and 58-124671. A wire dot matrix printer of another type in which, instead of such an ink absorbent member fixed in a printer head, an ink reservoir vessel having a projecting cloth-fiber cable wet with ink, projected therefrom and fixed thereon is removably mounted on the printer head so as to urge a projection end surface of the cloth-fiber cable against one-side surfaces of a plurality of vertically aligned printing wires, is disclosed in U.S. Pat. No. 4,445,127.
In the wire dot matrix printers of those types as described above, however, the forced contact portion between the ink absorbent member or cloth-fiber cable and the respective printing wires is not free from abrasion or deterioration by the reciprocating motion of the printing wires. Accordingly, sufficient inking to all the printing wires over a long period of time cannot be ensured. Furthermore, a friction load due to the forced contact is added to the printing wires in motion, and the load may varies for every printing wire. Consequently, smudgy or blurred printing is apt to occur.
3. Applications of Related Techniques Filed by the Present Inventors
In order to eliminate the above-mentioned defects in the prior art, T. Taguchi and T. Ishikawa of the inventors of this application invented techniques related to an inking system for a wire matrix printer in which ink absorbed in an ink absorbent member can be uniformly and sufficiently transferred to each of printing wires without forcedly urging the ink absorbent member against the respective printing wires. The invented techniques were applied for Japanese utility model registrations on July 31, 1984. The applications were laid open on Feb. 26, 1986 bearing Utility Model Unexamined Publication Nos. 61-31834 and 61-31835. Further, the invented techniques are disclosed in U.S. patent application Ser. No. 760,599 filed in the United States on July 30, 1985 claiming priority on the basis of the above-mentioned Japanese utility model applications and assigned to the assignee of this application. This inking system is featured in that a gap large enough to avoid friction is provided between each of or the whole of a group of printing wires and an ink absorbent member surrounding the printing wires and that the ink absorbent member is arranged to be urged by springs or the like against the rear surface of a bearing plate provided on the front end surface of a printer head for supporting the printing wires, so that ink absorbed in the ink absorbent member returns to its original liquid state on the rear surface of the bearing plate and the liquid ink is transferred to printing ends of the respective printing wires through holes formed in the bearing plate for slidably supporting the respective printing wires. In this inking system, the ink absorbent member is fixedly accommodated in an ink chamber provided at a nose portion of the printer head. An ink vessel for storing ink therein is adapted to be removably mounted on the upper portion of the ink chamber, and a capillary path member extending from the inside of the ink vessel downward to the lower outside of the same through the bottom thereof. The ink vessel is mounted at the upper portion of the ink chamber so that the projecting lower end surface of the capillary path member is made to be in forced contact with the upper surface of the ink absorbent member through an opening formed in the upper surface of the ink chamber. Thus, the ink can be supplied from the ink vessel to the ink absorbent member. Owing to the above-mentioned arrangement and functions, inking to the printing wires can be made surely without causing any deterioration or any abrasion in the ink absorbent member and without applying any additional frictional load to the printing wires in motion.
Further, M. Kobayashi, H. Fukui and T. Taguchi of the inventors of this application invented a technique as to an inking system for a wire dot matrix printer having an arrangement and functions which can be summarized as follows. This technique was applied for a Japanese utility model registration on July 31, 1984 and was laid open on Feb. 26, 1986 bearing Japanese Utility Model Unexamined Publication No. 61-31833. The inking system according to this technique is arranged such that a cartridge containing printing ink therein is removably mounted on the upper surface of a nose portion of a printer head. A capillary path member providing an ink path extending from the inside of the cartridge downward to the outside through the bottom of the same is integrally formed in the cartridge. A slit is formed at the projecting lower end portion of the capillary path member, the slit being opened at its lower portion to permit a group of printing wires to extend therethrough. An opening is formed in the upper surface of the nose portion for inserting the lower end portion of the capillary path member into the inside of the nose portion, so that the inner surface of the slit is made to be in contact with or to be close to each of the printing wires in the nose portion when the cartridge is mounted onto the nose portion. In such an arrangement, ink absorbed in the lower end portion of the capillary path member can be transferred to each of the printing wires through the direct contact between the lower end portion of the capillary path member and the respective printing wires or through the contact between the lower end portion of the capillary path member and the rear surface of a bearing plate fixed on the front end of the nose portion for supporting the printing wires.
In those two types of inking systems applied for utility model registration, problems to be improved were found as the results of a great deal of experiences of use thereafter. In the inking system disclosed in the above-mentioned U.S. patent application Ser. No. 760,599, the ink absorbent member is provided within the nose portion and fixed thereto. Therefore, when a printing operation is suspended for a long time, ink sludge is accumulated in the voids inside the ink absorbent member due to evaporization of ink contained in the ink absorbent member to thereby make the ink absorbent member clogged to bring a hindrance to absorption of ink into the absorbent member and to fluidity of ink inside the same. Furthermore, replacement of the ink absorbent member is not easy. These problems are the same as those in the prior art inking system in which the ink absorbent member is disposed within the nose portion and fixed thereto.
The inking system as disclosed in Japanese Utility Model Unexamined Publication No. 61-31833 is excellent in that the above-mentioned problems are solved in the system. This inking system is different from the inking system as disclosed in U.S. Pat. No. 4,445,127 in that the ink cartridge is filled with a fiber for reserving ink in an absorbed state, so that the lower end portion of the capillary path member can therefore be approached to the group of printing wires from just above, and ink supply from the capillary path member to the respective printing wires is effected from the opposite sides of the respective printing wires. In this inking system, however, the lower end portion of the capillary path member is deteriorated and worn out at a portion brought into forced contact with the printing wires. If the width of the slit permitting the printing wire group to extend therethrough is enlarged to avoid this defect, it cannot be ensured to supply ink completely to all the printing wires.